Different Enviroment Map per object/layer. (Blender Engine)
By using multiple scenes you can get the different parts and composite them together. Have one scene that renders the background you want, then another scene for the object with the environment you want reflected on it's surface, render this scene with the background as transparent then composite the objects onto the background.





You could setup multiple scenes to get different reflections for each object. The object index can help to mask out each object when compositing.